Lightweight reflecting structures utilizing magnetic deployment forces

ABSTRACT

The apparatus of the present invention provides an ultralightweight collapsible reflecting structure for electromagnetic wave energy that is primarily intended for space applications. The vast distances over which space systems must operate frequently dictate the use of antennas which are highly directional, which generally requires large reflecting structures of relatively close dimensional tolerances for focusing the electromagnetic radiation. The collapsible reflectors of the present case are provided by a precontoured flexible lightweight foil or screen which is deployed by the use of magnetic pressures generated by current loops or permanent magnets.

United States Patent Kurt Amboss;

Wolfgang Knauer, both of Malibu, Calif. 842,525

July 17, 1969 Sept. 14, 1971 Hughes Aircraft Company Culver City, Calif.

Inventors Appl. No. Filed Patented Assignee LIGHTWEIGHT REFLECTING STRUCTURES UTILIZING MAGNETIC DEPLOYMENT FORCES 5 Claims, 5 Drawing Figs.

U.S.Cl 343/915, 343/840, 343/897 1111. u ..H0lq 15/20, H01q 19/12,H01q 1/36 Field ofSearch 343/915,

[56] References Cited UNITED STATES PATENTS 3,224,007 12/1965 Mathis 343/915 3,420,469 1/1969 Johnson et al. 244/1 Primary ExaminerEli Lieberman Assistant ExaminerMarvin Nussbaum Attorneys-lames K. Haskell and Robert H. Himes PATENTED SEPI 419m 3,605.10?

sum 2 or z lizard LIGHTWEIGHT REFLECTING STRUCTURES UTILIZING MAGNETIC DEPLOYMENT FORCES BACKGROUND OF THE INVENTION Electromagnetic wave reflectors for space applications can be categorized into large and small structures. The term large" as applied to reflecting structures refers to structures having dimensions'ranging from several feet to several'hundred feet or more. For relatively small structures it is possible to adapt terrestrial designs to the environs of space. For example, a parabolic reflector having a diameter of a few feet may be provided by a rigid preassembled structure that may be deployed in space rather easily. Where relatively large reflectors are required, however, size and weight limitations prohibit the utilization of rigid preassembled structures.

Contemporary approaches for large structures contemplate the use of a number of ribs which are unfolded much like an umbrella and to which a reflecting membrane is attached. Another proposed device, sometimes referred to as a swirlabola, also utilizes riblike members which when furled are wound about a central hub and which when unfurled extend radially and support a metallized plastic or fabric reflecting surface. Both the umbrella and the swirlabola designs contemplate the use of prestressed or preformed beams or ribs. Such designs, when employed in large reflector applications, are subject to undesirable thermal deformation and concomitant changes in contour. I

A petaline or leaf-type reflector has also been proposed. This reflector utilizes preformed pie-shaped segments of fairly rigid sheet metal or metallized plastic. When furled, the pieshaped segments are stacked. When deployed, these segments rotate abut a central hub somewhat in the manner of a fan and are latched into place to form a paraboloid reflector. Again, such a design in large-scale applications is unsuitable, mainly because of the weight limitations brought about by the requirement for the high-stiffness segments, but also because of inherent thermal distortions.

It has also been proposed to utilize erectable antennas having a hollow bladderlike framework which, when deployed, is inflated by gas or foam. The framework thereby assumes a substantially rigid configuration which is supportive of a reflecting membrane. The close dimensional tolerances which are required for most applications, however, are extremely difficult to maintain with such a structure. In addition, this design shares with the other above-mentioned prior art designs the disadvantage of a somewhat high weight-to-size ratio for large diameters.

SUMMARY OF THE INVENTION In accordance with the present invention, a preferred embodiment includes a preformed mesh of lightweight electrically conductive members such as wires or conductively coated fibers. The mesh is supported at its periphery by an articulated ringlike structure. The preformed contour of the mesh is maintained by magnetic pressure. Magnetic deployment is provided by different approaches designated magnetostatic or electromagnetic. Magnetostatic deployment is defined as providing the required magnetic pressure by the interaction of a magnetic field, generated by permanent magnets, with other permanent magnets. Electromagnetic deployment, on the other hand, is defined as providing the magnetic pressure by the interaction of a magnetic field generated by current loops with the magnetic field generated by permanent magnets.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 illustrates a cross-sectional view of an antenna utilizing magnetostatic deployment;

FIG. 2 illustrates the stowed configuration of the strut sections, ring and feed pole of the antenna of FIG. I;

FIG. 3 shows the generation of the force vectors in the antenna of FIG. I:

' FIG. 4 is a schematic representation of an electromagnetically deployed antenna; and

FIG. 5 shows an enlarged portion of the deployed reflector in the device of FIG. 4.

DESCRIPTION Referring now to FIG. I of the drawings, there is shown a cross-sectional view of an antenna in accordance. with the present invention utilizing magnetostatic deployment. In particular, the antenna of FIG. 1 includes a contoured parabolic reflector screen 10 which is supported about the periphery thereof by means of an articulated tubular ring structure 12. The inner portion of the contoured reflector screen 10 terminates on a circular rigid center section 14 which provides a continuation of the parabolic configuration of the contoured reflector screen 10. The rigid center section 14 is supported by a rigid cylindrical tube 15 which is attached to a mounting bracket 16 which, in turn, is attached to a spacecraft, for example (not shown). The rigid cylindrical tube 15 houses a feed pole 18 which includes a rigid coaxial line 19 terminated by a dipole 20 and a reflector 21. The articulated ring structure 12 is supported by three collapsible struts 22, extending at uniform intervals from the mounting bracket 16 to the ring structure 12. In addition, a cone-shaped contoured screen 24 is disposed in back of the parabolic reflector screen 10 supported between the rigid cylindrical tube 15 and the articulated ring structure 12.

It is well known that conductive wire meshes have rf reflecting properties similar to the reflecting properties of solid conductive surfaces when the spacing between adjacent wires is a small fraction of a wavelength at the frequency of operation. It is thus possible to construct a reflecting surface therefrom. It has been found that thin quartz fibers coated with a very thin layer of aluminum are especially adapted for use in reflecting meshes. In addition to the very lightweight of such a mesh it is highly resistant to kinks and fractures, and once formed into a surface of a given shape, tends to maintain that shape to a high degree of accuracy.

In the particular case of the embodiment of FIG. I, reflector screen 10 can comprise such a conductive mesh in which the separation between adjacent conductive members or fibers is a small fraction of a wavelength at the highest frequency of intended operation. The cone-shaped screen 24 can comprise a similar mesh, except that the spacing between conductive members is not critical. In the alternative, cone-shaped screen 24 can also comprise a mesh of material which by ordinary standards may be considered a dielectric. In either case, reflector screen 10 and cone-shaped screen 24 are fabricated from nonmagnetic material.

In a copending application of J. H. Cover, .lr., R. K. Jenkins, and L. B. Keller, Ser. No. 590,571, filed Oct. 3l, 1966, and now abandoned, and assigned to the same assignee as is the present case, there is disclosed a method for fabricating a conductive mesh suitable for the above application. Briefly, the fabrication technique comprises the steps of laying a grid of conductively coated quartz fiber over a mandrel preformed in the shape of the desired reflecting surface. The intersections of the fibers are then bonded and the mesh removed from the mandrel.

In a terrestrial environment the forces, or more accurately the force per unit area (i.e., pressure), needed to maintain the contour of the reflector screen 10 must, in general, be sufficient to overcome gravitational forces as well as forces due to wind. In a space environment, however, the pressure required to maintain the contour of the reflector screen 10 is much smaller due to the lack of significant gravitational and wind forces. Of course, other forces and effects may be encountered by a magnetically contoured antenna in a space environment. To the extent that these environmental disturbing forces are believed to affect the operation of the various embodiments of the present invention, they will be discussed in greater detail hereinbelow.

The reflector support structure comprising the tubular ring structure I2 is attached to a satellite or spacecraft body by means of a tripod structure consisting of collapsible struts 22. In general, ring structure I2 and struts 22 are composed of a plurality of segments which are suitably hinged and slidably engaged so that they can be folded or telescoped into a compact package such as shown in FIG. 2, prior to deployment. The mechanical details of an articulated ring and collapsible struts suitable for this purpose are disclosed in a copending application of J. H. Cover, Jr., A. F. Fraser and B. R. Gaspari, Ser. No. 590,561, filed Oct. 31, 1966, and assigned to the same assignee as is the present case.

Referring again to FIG. I, numerous permanent magnetic needles 26 are disposed on the contoured reflector screen and an equivalent number of permanent magnet needles 28 are disposed on the cone-shaped screen 24. The permanent magnet needles 26, 28 may, for example, be fabricated of Alnico V-7 and have the dimensions 1 X 0.5 X 0.5 cm. The number of needles 26, 28 required on screens 10, 24 are determined by the deployment force needed to overcome the elastic screen forces. For a contoured reflector screen of 30 feet diameter, for example, and a metallized quartz fiber screen mesh of 0.1-inch fiber spacing and 2 X IO -inch fiber diameter, which is suited for microwave operation up to 8,000 me., the elastic screen forces will not exceed 2 X 10 dynes/cmF. A deployment force in excess of 2 X 10 dynes/cm. to overcome the elastic screen forces can be provided by spacing the screens 10, 24 an average of about cm. from each other and by spacing also the needles 26, 28 an average of 20 cm. apart.

Referring to FIG. 3, the deployment forces, F, result from the magnetostatic dipole interaction between permanent magnet needles 26 and 28 which are consistently oriented with poles of opposite polarity at the extremities thereof nearest together. The interaction is described by the relation where k is the interaction force (in dynes), m is the magnetic moment (about 250 gauss cm. for Alnieo V-7 needles of l X 0.5 X 0.5 cm) and a is the distance between opposing needles (about 20 cm.).

Referring to FIG. 4, there is shown a schematic representation of an alternative embodiment of the invention, adapted to be electromagnetically deployed. In particular, the antenna of FIG. 4 includes a large paraboloidal reflector screen 34 supported at its periphery by a tubular ring structure 36. The screen 34 is accurately prefabricated as was reflector screen 10 whereby it can assume the deployed configuration with only modest deployment forces. In addition, permanent magnet needles 38 are bonded to the screen as shown in the en larged view of FIG. 5. The permanent magnet needles 38 are distributed uniformly over the entire area of the reflector screen 34 on the back side thereof with the north pole in contact therewith. The permanent magnet needles 38 may, for example, be fabricated of Alnico V-7 with the dimensions 0.5 X 0.15 X 0.15 emf. A current loop 42 is disposed adjacent to an antenna feed 44. The reference current loop 42 is oriented and current flow therein directed to generate a magnetic field approximating magnetic lines of force represented by dashed lines 45. Current flow through reference loop 42 generates the magnet field with magnetic lines of force represented by dashed lines 45. The reference loop 42 can either be made in one solid conductor or with a number of insulated turns. The number of needles 38 required on the surface of screen 34 and the current flow required through loop 42 are determined by the deployment force needed to overcome the elastic screen forces. For example, with an elastic screen force of 2 X 10 dynes/cmF, the combination of one permanent magnet needle 38 for every 10 cm. of surface area and a current flow of 500 ampere turns through current loop 42 provide a deployment force in excess of the required 2 X 10 dynes/cmf".

What is claimed is: l. A reflecting structure for electromagnetic wave energy comprising a reflecting screen of electrically conductive, flexi ble material, said screen being preformed to a predetermined contour having a concave side;

means attached to the periphery of said screen for supporting said screen about the periphery thereof;

numerous magnetic needles bonded to the back side of said screen over a substantial portion of the area thereof, said needles being poled in a uniform direction relative to said screen for generating a first magnetic field; and

means including a second interacting magnetic field for generating a force on said magnetic needles away from the concave side of said reflecting screen thereby to maintain said screen in said preformed contour.

2. The reflecting structure for electromagnetic wave energy as defined in claim 1 wherein said last-named means including a second interacting magnetic field for generating a force on said magnetic needles away from the concave side of said reflecting screen includes a conical screen disposed on said back side of said screen, and numerous additional magnetic needles bonded to said conical screen with the respective extremities thereof poled to a polarity opposite that of the nearest extremities of said magnetic needles bonded to said reflecting screen.

3. The reflecting structure for electromagnetic wave energy as defined in claim 1 wherein said last-named means including a second interacting magnetic field for generating a force away from the concave side of said reflecting screen on said magnetic needles constitutes no less than one loop of conductor and a current source connected theretov 4. A lightweight antenna adapted to be attached to a moving vehicle, said antenna comprising a rigid circular element for providing a conductive surface having the contour of the center portion of a paraboloid of predetermined focal length, said paraboloid having a circular intersection with a plane normal to the axis of rotation thereof at a selected point therealong, said circular intersection having a diameter substantially greater than that of said rigid circular element;

a ring structure having a diameter equal to that of said circular intersection mechanically supported about said axis of rotation at said selected point therealong;

a conductive flexible mesh of preformed paraboloidal contour having a focal length equal to said predetermined focal length extending from the outer periphery of said rigid circular element to said ring structure;

an additional flexible mesh of preformed conical-shaped contour extending from said ring structure to said axis of rotation at a point therealong on the concave side of said paraboloidal contour; and

numerous permanent magnet needles attached to said conductive flexible mesh and said additional flexible mesh, respectively, symmetrically about said axis of rotation, said permanent magnet needles on said conductive flexible mesh being poled to attract said permanent magnet needles on said additional flexible mesh, thereby to maintain said conductive flexible mesh in said preformed paraboloidal contour.

5. The lightweight antenna as defined in claim 4 wherein said ring structure is articulated in a manner to allow it to be collapsed with said conductive flexible mesh and said additional flexible mesh attached thereto. 

1. A reflecting structure for electromagnetic wave energy comprising a reflecting screen of electrically conductive, flexible material, said screen being preformed to a predetermined contour having a concave side; means attached to the periphery of said screen for supporting said screen about the periphery thereof; numerous magnetic needles bonded to the back side of said screen over a substantial portion of the area thereof, said needles being poled in a uniform direction relative to said screen for generating a first magnetic field; and means including a second interacting magnetic field for generating a force on said magnetic needles away from the concave side of said reflecting screen thereby to maintain said screen in said preformed contour.
 2. The reflecting structure for electromagnetic wave energy as defined in claim 1 wherein said last-named means including a second interacting magnetic field for generating a force on said magnetic needles away from the concave side of said reflecting screen includes a conical screen disposed on said back side of said screen, and numerous additional magnetic needles bonded to said conical screen with the respective extremities thereof poled to a polarity opposite that of the nearest extremities of said magnetic needles bonded to said reflecting screen.
 3. The reflecting structure for electromagnetic wave energy as defined in claim 1 wherein said last-named means including a second interacting magnetic field for generating a force away from the concave side of said reflecting screen on said magnetic needles constitutes no less than one loop of conductor and a current source connected thereto.
 4. A lightweight antenna adapted to be attached to a moving vehicle, said antenna comprising a rigid circular element for providing a conductive surface having the contour of the center portion of a paraboloid of predetermined focal length, said paraboloid having a circular intersection with a plane normal to the axis of rotation thereof at a selected point therealong, said circular intersection having a diameter substantially greater than that of said rigid circular element; a ring structure having a diameter equal to that of said circular intersection mechanically supported about said axis of rotation at said selected point therealong; a conductive flexible mesh of preformed paraboloidAl contour having a focal length equal to said predetermined focal length extending from the outer periphery of said rigid circular element to said ring structure; an additional flexible mesh of preformed conical-shaped contour extending from said ring structure to said axis of rotation at a point therealong on the concave side of said paraboloidal contour; and numerous permanent magnet needles attached to said conductive flexible mesh and said additional flexible mesh, respectively, symmetrically about said axis of rotation, said permanent magnet needles on said conductive flexible mesh being poled to attract said permanent magnet needles on said additional flexible mesh, thereby to maintain said conductive flexible mesh in said preformed paraboloidal contour.
 5. The lightweight antenna as defined in claim 4 wherein said ring structure is articulated in a manner to allow it to be collapsed with said conductive flexible mesh and said additional flexible mesh attached thereto. 